1. Field of the Invention
The present invention relates to a cleaning composition for stripping and removing a resist film, resist residue, and other reaction residue left by an etching gas (i.e., etching residue) that remain on a semiconductor substrate after dry etching in forming a metal interconnection having copper as its main component, and a method of manufacturing a semiconductor device using the same.
2. Description of the Background Art
Generally, in a process of manufacturing a highly integrated semiconductor elements, a resist film is first applied on an interconnection material such as a metal film which becomes an interconnection for electric conduction, and on an interlayer insulating film material which ensures insulation between interconnections. A desired resist pattern is formed by photolithography, and dry etching is conducted using the resist film as a mask, and then the remaining resist film is removed. To remove the resist film, it is common to perform wet treatment after plasma ashing, to strip and remove resist residue remaining on the interconnection material and the interlayer insulating material using a cleaning composition.
With an aluminum-based interconnection material conventionally used, examples of the cleaning composition therefor include: fluorine type compound-based cleaning compositions (Japanese Patent Laying-Open Nos. 7-201794, 8-202052, 11-271985), a cleaning composition containing hydroxylamine (U.S. Pat. No. 5,334,332), and a cleaning composition containing quaternary ammonium hydroxide (Japanese Patent Laying-Open No. 7-247498).
With advancement of downsizing and speeding of semiconductor elements in recent years, however, the manufacturing process of the semiconductor devices has been changed considerably. For example, to fulfill the demand for speeding of the semiconductor elements, Al or Al alloy conventionally used as the interconnection material has been replaced with Cu or Cu alloy having lower electric resistance than Al or Al alloy, and p-TEOS (Tetra Ethyl Ortho Silicate) film or the like conventionally used as the interlayer insulating film has been replaced with a so-called Low-k film having a lower dielectric constant than the p-TEOS film. Examples of the Low-k film currently regarded as promising include: a film formed of inorganic material such as porous silica or the like, a film formed of organic material such as polyimide, polyarylene or the like, and a film formed of a mixture of the above-mentioned inorganic and organic materials.
Further, with advancement of downsizing, an i-line resist conventionally used in the photolithographic process has been replaced with a chemically amplified excimer resist, such as KrF excimer resist, ArF excimer resist or the like, and a highly efficient cleaning composition corresponding thereto has been demanded.
Problems of the conventional cleaning composition and the method of manufacturing a semiconductor device using the same are now described with reference to FIGS. 3A-3K.
An element such as a transistor (not shown) is formed on a semiconductor substrate. Referring to FIG. 3A, a first copper interconnection 1 of an embedded type is formed in a first insulating film 2 using a known damascene process. A silicon nitride film 3 as a protective film of the copper interconnection and a Low-k film 4 as an interlayer insulating film of a low dielectric constant are successively formed thereon, and a resist film 5 patterned to a prescribed shape is formed further thereon. Here, a chemically amplified excimer resist corresponding to, e.g., KrF excimer laser exposure or ArF excimer laser exposure is employed as the resist material.
Next, referring to FIG. 3B, Low-k film 4 is dry etched, using resist film 5 as a mask, to expose silicon nitride film 3, so that a via hole 21 is formed. At this time, reactive products of the gas used for the dry etching and the Low-k film and the resist film accumulate in via hole 21 as resist residue 6.
Next, referring to FIGS. 3B and 3C, resist film 5 is removed by plasma ashing. At this time, a modified film 7 is formed at the surface of Low-k film 4 according to the reaction of heat and plasma during ashing.
Next, referring to FIGS. 3C and 3D, resist residue 6 is removed by processing with a conventional fluorine type compound-based cleaning composition. Any remaining resist residue would cause electrically loose connection with an upper interconnection to be formed afterward. Thus, to ensure the removal of the resist residue, the cleaning composition likely to etch even the insulating film has been used. As a result, modified layer 7 at the surface of the Low-k film as well as the Low-k film 4 itself have been etched, resulting in via hole 21 of an enlarged internal diameter.
Thereafter, referring to FIG. 3E, a resist film 5 patterned for trench formation is formed on Low-k film 4 to form an interconnection to be connected with via hole 21.
Next, referring to FIG. 3F, Low-k film 4 is dry etched, using resist film 5 as a mask, down to its intermediate position to form a trench 22. At this time, resist residue 6, being a reaction product of the gas used for the dry etching, and the Low-k film, accumulates in via hole 21 and trench 22.
Next, referring to FIGS. 3F and 3G, resist film 5 is removed by plasma ashing. At this time, a modified layer 7 is formed at the surface of Low-k film 4 according to the reaction of heat and plasma during ashing.
Next, referring to FIGS. 3G and 3H, resist residue 6 is removed by processing with a conventional fluorine type compound-based cleaning composition. The conventional cleaning composition removes the resist residue and also etches modified layer 7 at the surface of the Low-k film, so that the internal diameter of via hole 21 is enlarged and the width of trench 22 increases.
Next, referring to FIG. 3I, silicon nitride film 3 is removed by dry etching to expose first copper interconnection 1. At this time, etching residue 8 accumulates in via hole 21.
Next, referring to FIG. 3J, the surface of the copper interconnection is cleaned with the cleaning composition. With the conventional fluorine type compound-based cleaning composition, first copper interconnection 1 would be corroded if the removing action of resist residue and other etching residue is enhanced. Thus, a copper corrosion inhibitor such as benzotriazole (BTA) has been added to prevent corrosion of the first copper interconnection (Japanese Patent Laying-Open No. 2001-83712). With such a cleaning composition, however, there is a problem that the copper corrosion preventing effect would be degraded when it is attempted to further improve the resist residue removing action.
Next, referring to FIG. 3K, copper is filled in via hole 21 and trench 22 by plating or the like. A second copper interconnection 10 is then formed by CMP (Chemical Mechanical Polishing). If the first copper interconnection 1 has been corroded by the conventional cleaning composition, however, the second copper interconnection 10 cannot fill via hole 21 completely. In such a case, junction resistance between the first copper interconnection 1 and the second copper interconnection 10 becomes high, or they may even be disconnected.
An interval 11 between the interconnections has become narrow with downsizing of the elements. If the conventional cleaning composition is used for the above-described process, modified layer 7 at the surface of the Low-k film as well as the Low-k film 4 itself would be etched to further narrow the interval 11 between the interconnections. This would cause degradation in characteristics, such as a decrease of operating speed of a semiconductor element due to increased electric capacitance between the interconnections, or a defect such as a short-circuit between the interconnections. Further, with the conventional cleaning composition, complete removal of resist residue as well as corrosion control of both copper and the Low-k film are not obtained.